Modern electronic equipment uses analog semiconductor integrated circuits for operation thereof. The analog semiconductor integrated circuits receive analog inputs from various sources, e.g., analog voltage signals such as from sensors, a current-to-voltage converter (resistor), etc., and/or may output analog voltage levels, e.g., analog meter, audio and video applications, servo control, etc. Typically, analog signals must be amplified and/or isolated from an input or an output, and may require impedance transformations from a very high impedance source to driving a low impedance load. Analog operational amplifiers are well suited to perform the aforementioned functions since they are low cost and easily configured for a desired gain with just a few basic parts. Operational amplifiers have become so popular that they are available in many of the standard integrated circuit packages with a substantially uniform pin-out for each of these integrated circuit packages.
Generally, the voltage gain of an operation amplifier may be defined by one or two resistors. So an electronic system using analog input and/or output signals and requiring analog amplification, isolation and/or impedance matching may comprise a plurality of operational amplifiers and gain setting resistors associated therewith. Operational amplifiers in integrated circuit packages are space efficient when used in high density printed circuit boards, however, the gain setting resistors, even the surface mount style, are generally discrete components and take up a lot more circuit board space for what they contribute to the overall electronic system.
Programmable gain operational amplifiers are available that do not require any external gain setting resistors, however, these programmable gain operational amplifiers are generally more complex and are designed for more sophisticated and complex applications than a standard operational amplifier. In addition, the programmable gain operational amplifiers may be packaged and have different pin-outs, e.g., additional pins for gain control, then standard operational amplifiers, and thereby cannot be used as direct replacements in existing electronic circuit board designs. The programmable gain operational amplifiers are generally more expensive than standard operational amplifiers because of their more complex circuitry and lower manufacturing volume compared to the costs and volumes of standard operational amplifiers.
Therefore, what is needed is an analog amplifier in an integrated circuit package that does not require gain setting resistors, has gain selection options and is compatible with existing printed circuit board layouts and integrated circuit package pin-outs.